Since the wave gear drive was invented by C. W. Musser (Patent Reference 1) to the present day, various types of wave gear drives have been invented by many researchers, including Musser and the inventor of the present application. Various inventions have also been proposed relating just to tooth profiles of wave gear drives. For example, the inventor of the present application has proposed making the basic tooth profile an involute tooth profile (Patent Reference 2), and a method of designing a tooth profile in which the tooth addendum profiles for wide contact between the rigid internal gear and the flexible external gear are derived using a rack approximation of the meshing between the two gears (Patent References 3 and 4). There has also been proposed an invention for avoiding interference between rack-approximated tooth profiles (Patent Reference 5).                Patent Reference 1: U.S. Pat. No. 2,906,143        Patent Reference 2: JP 45-41171 B        Patent Reference 3: JP 63-115943 A        Patent Reference 4: JP 64-79448 A        Patent Reference 5: JP 7-167228 A        